Separation control for record media transducer with transverse slots to supply ambient pressure

ABSTRACT

Means for improving separation between a transducer operating surface and a moving record media. Nonuniform pressure distribution between the media and the operating surface produces a cocking tendency in the media increasing upstream separation and decreasing downstream separation over the processing zone in the transducer. This invention recognizes that the cocking tendency is caused by a region of lower than ambient pressure near the point where the media draws away from the operating surface, and provides means for supplying ambient pressure at that point. In a preferred embodiment, the means comprises a transverse slot extending beyond the side edges of the media.

United States Patent Nor-wood 1 1' Feb. 15, 1972 s41 SEPARATION CONTROLFOR RECORD OTHER PU BucATmNs MEDIA TRANSDUCER WITH v TRANSVERSE Sims ToSUPPLY is ioiiil buil'fi'i ffig13 5 533 Head AMBIENT PRESSURE R. E,Norwood, E ffects of l 3er1ding Stiffness in Magnetic {72] Inventor;Rich! "Wood, Boulder, (3010 'zlggtgmlgBwlll/l .lzurgz lg of Research andDevelopment. pp.

are l 1 AS91811! minim 3m MM mn- J. T. S. Ma, An Investigation ofSelf-Acting Foil Bearings. monk Transactions of the ASME, Journal ofBasic Engineering. 221 Filed: Apr. 14, 1969 PePr .H 1965- [21] Appl.No.: 815,562 Primary Examiner-Tare" W. Fears Assistant Examiner-AlfredEddleman' At! -Hanif dJ d S. [52] US. CL ..l79/ 100.2 P, 179/ 100.2 C,340/ 174.1 E, omey m an anew an Roger Smith 1 340/1741 F [57] ABSTRACT[51] Int. Cl. ..Gllb5/22,Gl1b 5/60 58 Field inseam"... 179/100.2 P,100.2 PM; Means 'mPmvmB F ""F 340/1741 E, 174.1 F; 226/49, 97; 274/11 1)ag a? 23? g z il 7 ee e rn 1a an opera 111g su ace [56] chm Cmd producesa cocking tendency in the media increasing upv stream separation anddecreasing downstream separation Over UNITED STATES PATENTS theprocessing zone in the transducer. This invention recognizes that thecocking tendency is caused by a region Of lower 3,533,058 10/1970Platter ..l79/ 100.2 P than ambient pressure near the point where themedia draws 3,161,120 1964 Tim 6 79/ 2 P away from the operatingsurface, and provides means for sup- ,2 1966 179/1002 P plying ambientpressure at that point. In a preferred embodi- 3,319,238 7 Jacoby340/1741 E rnent, the means comprises a transverse slot extending beyond3,398,870 8/ 1968 Mullan et 81.... 1 79/ 100.2 P th ide edge Qfthe media3,435,442 3/1969 Ma et a] ..l79/100 2 P 3,582,917 6/1971 Hertrich..340/174.1 E 4 Claims, 7 Drawing Figures PATENTEDFEB1 5 I972 sum 1 [1r2 FIG. 1

INVENTOR RICHARD E. NORWOOD 8% FIG. 2

FIG. 3

ATTORNEY PATENTEDFEHISIQYE snwzurz FIG.5

SEPARATION CONTROL FOR RECORD MEDIA TRANSDUCER WITH TRANSVERSE SLOTS TOSUPPLY AMBIENT PRESSURE BACKGROUND OF THE INVENTION The presentinvention relates to magnetic transducer apparatus, and moreparticularly to flexible web record media transducers of the type whichemploy fluid bearings between the operating surface of the transducerand the moving media to reduce wear and control separation. 1

The use of fluid bearings between moving magnetic record media, such asmagnetic tape, and a transducer employed to write on or read from themedia, has become popular in recent years. Techniques for generatingsuch bearings and controlling their thickness are taught in US. Pat. No.3,l70,045 and U.S. Pat. No. 3,416,148, both assigned to the assigneehereof. The techniques described involve passing the media over a curvedoperating surface to develop a bearing whose thickness is a function ofvarious parameters, including the curvature of the surface, record mediavelocity, the angle of wrap and tension on the media, and the viscosityof the fluid from which the bearing is created. The patents furtherpoint out that the stability of the bearing and the uniformity of its.thickness are, in part, a function of the arc length over which itexists along the operating surface of the head. The present invention isconcerned with situations wherein it is desirable to provide a uniformfluid bearing over a length of operating sur- .face, but where the wrapangle and operating surface contour are such, with respect to the mediainvolved, that a constant pair of generally flat surface portions thatare inclined only a few degrees relative to one another and are joinedby a small ,radius portion. The record media assumes an angle of wrapover the radius portion and a bearing is generated, but, due to theshort arc length involved, precise control and stability are difficultto achieve. It is found that the bearing developed in this case oftenvaries in thickness along the radius portion. It is also found that thepoint of closest proximity between the radius portion and the mediashifts, depending upon the direction the media is travelling. If atransducing gap is located in the radius section, these variations cancause variations in the signals recorded on or read from the media bythe gap. Unless the gap is located precisely midway between the pointsof closest proximity for each direction of media travel, a differentseparation is found at the gap for each direction of motion anddifferent transducing action takes place. A magnetic tape read in theforward direction of tape motion in this situation will producedifferent signal strengths than when read in a backward direction.

It isimportant in a present day magnetic tape processor that theforward-backward" ratio of transduced signal characteristics bemaintained as nearly equal to 1:1 as possible for error-free operation.Accordingly, it is the principal object of this invention to provide, ina transducer having transducing gaps located in radius portions of itsoperating surface, means for stabilizing the fluid bearing between themoving record media and the radius surface, and for ensuring uniformityof its thickness. It is a particular object of the invention to improvethe uniformity of the bearing thickness for both directions of motion ofthe media.

SUMMARY OF THE INVENTION An important aspect of this invention is thediscovery that a flexible record media of a given stiffness, such as aconventional magnetic tape, passing over a radius on an operatingsurface, generates fluid bearing pressure, the distribution of which isnot symmetrical between the entry and exit points of tangency betweenthe media path and the surface. In actuality, the moving mediadoes notleave the surface at the exit point of tangency determined byits wrapangle, but tends to follow the surface further than it should. Analysisof the pressure distribution between the mediaand the surface has shownthat this situation results from the presence of a negative pressureregion near the exit point of tangency. This negative pressure regionseems to be produced by the increase in the volume of the space betweenthe media and the surface as the media leaves the surface, and aninability of the environmental fluid to till the space adequately underthe conditions present. The media is, accordingly, drawn toward thesurface and cocked downstream. In cases where the wrap angle is smalland the length of the fluid bearing is short, the cocking contributes tononuniformity' of separation over the distance between the entry andexit tangency points. It produces a varying separation that has aposition of closest proximity nearer the exit tangent point than theentry tangent point. This closest proximity position, thus, differs foreach direction of motion of the media and produces an undesirableforward-backward signal ratio, as earlier described, unless thetransducing gap on the radius surface is positioned exactly midwaybetween the two tangency points. Such fine positioning is difficult, ifnot impossible, to obtain.

According to this invention, the cocking problem is solved by providinga slot in the operating surface of the transducer at the position wherethe negative pressure region is found to have existed. The slot extendstransversely of the direction of motion of the media and communicateswith the ambient fluid environment at the sides of the media. Its widthand depth dimensions are sufficient to produce ambient pressure betweenthe media and the surface at the exit tangency point, thus dissipatingthe negative pressure region and allowing the media to depart along thepath dictated by the wrap angle. It has been found that, by provision ofthis slot, the tendency to cock is. eliminated and the fluid bearingover the length of operating surface between the entry and exit tangencypoints is greatly enhanced in terms of stability and uniformity ofthickness. Criticality of location of the transducing gap is thuseliminated. By providing a slot at each side of the transducing gap,located to prevent cocking for both directions of travel of the media,uniformity of separation in both forward and backward operation modes isachieved and a forwardbackward ratioof substantially l :l is achieved.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic representation of a transducer having atransducing gap positioned in a radius portion of its operating surface,and illustrating the cocking tendency of a record tape passed thereoverat a small wrap angle;

FIG. 2 is a plot of the fluid bearing pressure distribution between thetransducer operating surface and the record tape of FIG. 1;

FIG. 3 is a plot of the separation between the tape and operatingsurface of FIG. 1;

FIG. 4 is a schematic representation of a transducer similar to that ofFIG. I, but having slots provided in accordance with this invention;

FIG. 5 is a plot of the fluid .bearing pressure distribution between thetransducer operating surface and the record tape of FIG. 4;

FIG. 6 is a plot of the separation between the tape and operatingsurface of FIG. 4; and

FIG. 7 is a schematic representation of a transducer having pluraltransducing gaps spaced along the direction of tape motion showing theprovision of slots for each gap-containing area of the operatingsurface.

DETAILED DESCRIPTION Referring now in detail to the drawings, FIG. 1shows an enlarged elevational view of the contour of a portion of atransducer 10 having an operating surface 12 over whicha magnetic recordtape is passed. The surface 12 has a width dimension (into the plane ofthe paper) at least equal to and preferably greater than the width ofthe record tape and is generally smooth and continuous over the lengthshown. As illustrated in FIG. 1, the surface includes a radius portion14 that blends at each end with two generally flat portions 16 and 18that are inclined one to the other. The radius portion 14 comprises aprocessing zone of the transducer structure and a transducing gap 20 ispositioned within it. The magnetic head element that forms the gap ispartially shown in dotted outline at 22.

A magnetic record tape to be processed is passed over the operatingsurface along the path indicated by the solid line 24. As may be seen,the path of the tape is such that a small wrap angle over the radiusportion 14 is achieved. The wrap angle is provided by means (not shown)that cause the tape to enter and leave the processing zone of thetransducer at the angle shown. The means may include tape guides orfluid pressure means that constrain the tape. Its specific configurationis not a part of this invention and will not be described herein.

In accordance with the principles described in the patents mentionedearlier herein, passage of the tape along path 24 over the operatingsurface 12 produces a fluid foil bearing between the tape and thesurface 12 from the environmental fluid in which the apparatus resides(for example, air). The bearing produces a separation between the tapeand the surface 12 that lubricates the system and prevents excessivewear on both elements. The thickness of the bearing has been greatlyexaggerated in the drawings for the purposes of illustration; it is, inreality, usually in the order of 30-100 microinches, depending upon theseveral parameters which control its generation.

The fluid bearing generated in the arrangement shown existssubstantially over the arc length between the points where the tape path24 becomes tangent to the radius portion 14 of the surface 12. Thesepoints are identified in FIG. 1 at the intersections 26 and 28 of radiuslines R with the path 24. Depending upon the direction of travel of thetape, one of the points 26 or 28 is an entry point of tangency and theother is an exit point of tangency. These points of tangency are locatedwith respect to the static or desired tape path determined by its wrapangle. It will be appreciated from the following description that thetape does not always follow the preferred path, however, and tends toenter and leave the processing zone at points which vary from the pointof tangency. It is desirable that the bearing between the points oftangency be stable and uniform in thickness so that the tape followsessentially the preferred path 24 and good uniform transducing actioncan be achieved between the tape and the gap 20. It has been found,however, that in arrangements such as is shown, where conventional tapeis used and where the wrap angle is small (for example, in the order ofabout 10 or less) and the radius of curvature of the portion 12 is alsosmall (for example, less than one inch), there is not a sufficient arclength between points 26 and 28 to ensure a good stable and uniformbearing over the processing zone. It has been discovered that, for agiven direction of travel, the tape actually cocks downstream somewhat,assuming paths shown at 30 and 32 in FIG. 1. Path 30 is assumed for aleft to right direction (arbitrarily called forward," hereinafter) oftravel, while path 32 is assumed for the reverse (backward) direction.

This cocking has been discovered to result from a nonsymmetricalpressure distribution between the tape and the operating surface. Thatpressure distribution is shown in FIG. 2. The horizontal axis of theplot of FIG. 2 corresponds in scale to FIG. 1. Two curves 34 and 36 areshown. Curve 34 shows the pressure distribution for forward travel, andcurve 36 shows the distribution for backward travel. It will be seenthat, for each direction, there exists a positive pressure region over asubstantial length of the operating surface between the points oftangency 26 and 28, and then a negative pressure region (indicated by adip of the curve below the horizontal axis) at about the exit point oftangency where the tape should pull away from the surface 12. Thisnegative pressure region seems to be produced by an inability of theambient fluid to adequately flow into the increasing space beneath thetape under the conditions present when the tape is moving at high speed.The net result is that the negative pressure region draws the tape downat the exit point and moves the point of tangency downstream. The effectalso tends to move the entry point of tangency downstream and results inthe cocked condition shown by lines 30 and 32. The extent of the cockingeffect. and the exact position of the negative pressure region are afunction, in part, of the tape stiffness and may vary somewhat fordifferent tapes.

The amount of cocking in each case is exaggerated in FIG. 1 forillustration purposes. It is more accurately shown by thetape-to-operating surface separation plot of FIG. 3. In this plot, thecurves 38 and 40 illustrate the variation in separation of the tape forforward (curve 38) and backward (curve 40) travel with respect to thesurface of portion 14. The horizontal scale of FIG. 3 corresponds tothat of FIGS. 1 and 2 to permit ready comparison. Examination of FIG. 3shows that, for each direction of travel, the separation distance varieswidely between the entry and exit points of tangency, and includes apoint of closest proximity that is not positioned midway between thetangency points, but is moved downstream toward the negative pressureregion. It will be apparent from inspection of the curves 38 and 40that, unless the transducing gap 20 is precisely positioned at the exactcenter of the length of operating surface between the points 26 and 28,different separation will exist at the transducer for each direction oftape motion and an undesirable forward-backward signal ratio is found.In FIG. 1, the position of the gap 20 is shown as being offcenterslightly. The separation distances at the gap position for eachdirection of motion are shown by the intersections of curves 38 and 40with the line 42in FIG. 3.

Exact positioning is, of course, not possible within ordinarymanufacturing techniques. Additionally, some variation of the separationcurves 38 and 40 occurs during operation of the apparatus due to variouschanges in tape stiffness, wear, etc., so separation differences fordifferent tape motion directions will still exist.

The problems discussed in connection with FIGS. 1 through 3 are solvedin accordance with this invention by the provision of means to eliminatethe substantial negative pressure region between the tape and theoperating surface, and thereby eliminates the cocking tendency of thetape as it travels over the processing zone. The means comprises a slotin the operating surface extending transversely of the directions ofmotion of tape travel. FIG. 4 shows a transducer 10 like that of FIG. 1having slots 44 and 46 provided therein for this purpose. Each slot 44or 46 extends across the operating surface 12' of the transducer 10 adistance at least greater than the width of the tape and, preferably,from one side edge of the transducer to the other. FIG. 7 shows, inperspective, the arrangements of such slots at 116, in a completetransducer assembly.

The purpose of the slots 44 and 46 is to provide means to produceambient fluid pressure at the points where the deleterious negativepressure is found to exist. Accordingly, they must be of sufficientdepth and width to carry the volume of fluid required for this purposeand they must communicate with the ambient fluid at the sides of thetape. While two slots are shown in FIG. 4, it will be appreciated that,for a given direction of motion, the downstream slot is of primaryinterest. Thus, for forward motion, slot 46 provides the anticockingcontrol, while slot 44 controls the effect for backward motion. Thepositioning of the slots is important. For each direction of motion, theslot must be within the area of the operating surface portion at whichthe negative pressure is found to have existed. Generally speaking, thisis near the exit point of tangency. From the plot of FIG. 2, it will beseen that the negative pressure region extends upstream from the exittangency point 28' (forward) or 26' (backward) somewhat, so it is usefulto locate the upstream edge 44A or 46A of the slot somewhat inside thatpoint. Some variation in positioning may be permitted so long as theslot's upstream edge 44A or 46A is within the negative pressure area andcapable of equalizing the pressure enough to prevent cocking.Experimentation on a given operating surface contour to establish thenegative pressure point will establish the proper position for thatcontour.

As previously mentioned, the presence of two slots 44 and 46 providesfor elimination of the cocking problem in each direction of tape motion.The upstream slot is not essential for a given direction and, in atransducer arranged only for unidirectional tape motion operation, itmay be eliminated. It has been found, however, that such a slot isbeneficial in that it tends to bleed off some of thefluid that isdragged beneath the tape to form the fluid bearing and aids in producingthin bearings that improve transducing action. As described in thepatents mentioned earlier herein, the bearing thickness is directlyproportional to the radius of curvature of the operating surface in thearea where the bearing is generated. Accordingly, by bleeding off someof the fluid via the upstream slot to reduce the-thickness, larger radiiof curvature can be provided without production of excessively thickbearings, and the pressure loading on the tape and operating surface canthereby be minimized. This last relationship can be understood byconsidering that the pressure is proportional to the tape tension perunit width, divided by the radius of curvature.

FIG. 5 shows the pressure distribution between the tape and operatingsurface in the embodiment of FIG. 4. It will be noted that the negativepressure region has been effectively eliminated by the slot 46 forforward motion (curve 34') and by the slot 44 for backward motion (curve36'). Reference to FIG. 6 shows that the separation of the tape from theoperating surface is substantially constant along the processing zone,

' providing an equal separation for each direction of motion at thetransducing gap The tape, then, is found to travel substantially alongthe path 24 of FIG. 4 without any objectionable cocking tendency ineither direction. The necessity for precise gap location is eliminatedand any location within the land area 48 of the surface 14' betweenslots 44 and 46 is acceptable.

The slots 44 and 46 are a preferred means for supplying ambient fluidpressure beneath the tape at the negative pressure regions. It should beunderstood, however, that other equivalent means, such as holes in theoperating surface at the points where the slots 44 and 46 are shown,would suffice. Such holes would, of course, communicate with a sourceofambient pressure. v t

Although actual dimensions of thevarious elements are not considered tobe necessary for an understanding of the invention, and will vary widelydepending upon the transducing requirements of a given recordmedia-processing system, there are given below the general parameters ofthe embodiment shown in FIG. 4. This transducer is intended to operatewith a conventional half-inch magnetic record tape travelling at 200inches per second, with air as the fluid environment.

. R 0.5 inch.

Land Area 48 0.04 inch between slots 44 and 46.

Angle of Wrap 7".

Slots 44 and 46 0.006 inch deep and 0.04 inch wide (from upstream wallto downstream wall)..

Average tape-to-surface separation at gap 20' microinches.

FIG. 7 of the drawings is a perspective illustration of a multitracktransducer 100 provided in accordance with the principles of thisinvention. As may be seen, the transducer 100 has two transducing gaps102 and 104 in each information chanhe] or track along its operatingsurface 106. The purpose of the two gaps in each track is to permitsimultaneous writing and reading operations, as is well understood inthe art. The.

operating surface 106 is arranged to have a flat central portion 108with flat leading and trailing portions 110 and l 12 extending outwardlyin each direction at an angle thereto. The portions and 112 are bind tothe central portion by small curved portions "4 o radius r within whichthe transducing gaps are located. The portions 114 correspond to theradius portions 14 of FIG. 4. Near the points where each radius portion114 joins each of its adjacent flat portions, a slot ll6 is provided.The slots 116 provide the functions described with respect to slots 44and 46 of FIG. 4, and they are located near the points of tangency ofthe tape path with the radius portions 114 to relieve the negativepressures earlier described. In this transducer 100, the tape actuallyexperiences the situation described with reference to FIG. 1 twiceduring its travel over the operating surface 106; once as it is wrappedover each radius portion "4 between the center flat surface 108 and oneof the end flat portions 110 and I12.

Near the opposite ends of the'portions 110 and 112, additional slots 118are seen in FIG. 7. These slots are coupled to a source of vacuumpressure and operate to load the tape (not shown) downwardly over thetransducer 100 to create the wrap angle necessary for generation offluid bearings at the radius portions 114 and control of the tapeseparation at the transducing gaps. Longitudinal slots 120 extend towardthe radius portions from the vacuum slots 118. These slots 120 arepositioned to underlie the side edges of the tape as it passes over thetransducer and exerta downward force to prevent any tendencyof the edgesto curl upwardly.

Additional longitudinal intertrack slots 122, may be provided in atransducer 100 to provide a channelling action for a portion of thefluid bearings over the surfaces 114 to further reduce theirthicknesses. The function of the slots 122 in no way adversely affectsthe anticocking action of slots 116.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. In a magnetic tape transducer of the fluid bearing type which has anoperating surface including a radius portion connecting inclined flatsurface portions over which a length of magnetic tape, significantlengths of which appear flexible and short lengths of which appearrigid, having a fixed width is adapted to be moved in either of twodirections, said tape being arranged to have an angle of wrap about theradius portion of the operating surface that produces spaced entry andexit points of tangency with said surface for each direction ofmovement, and wherein movement of the tape over said operating surfacegenerates a fluid bearing between said tangency points, the improvementin means for providing a uniform bearing over a substantial portion ofsaid operating surface between said points of tangency for eachdirection of tape motion, comprising a slot, extending transversely ofthe direction of tape motion, immediately adjacent said exit point oftangency, within a distance from said exit point corresponding to ashort length of apparently rigid tape, and substantially longer than thetape width for supplying ambient fluid pressure between the tape and theoperating surface when the tape is moving in a direction toward saidexit point of tangency from the entry point of tangency 2. The inventiondefined in claim 1, wherein the transverse slot has a cross-sectionalarea sufficient to produce ambient fluid pressure throughout its volume.

3. The invention defined in claim 2, wherein there are two of said slotsextending transversely of the direction of tape motion and positionedbetween the spaced-apart entry and exit points of tangency.

4. The invention defined in claim 3, wherein the magnetic tape is aconventional one-half-inch-wide record tape of average stiffness,wherein the radius portion of the operating surface has a radius of lessthan one inch, and wherein the angle of wrap is less than 10.

' l I? t

1. In a magnetic tape transducer of the fluid bearing type which has anoperating surface including a radius portion connecting inclined flatsurface portions over which a length of magnetic tape, significantlengths of which appear flexible and short lengths of which appearrigid, having a fixed width is adapted to be moved in either of twodirections, said tape being arranged to have an angle of wrap about theradius portion of the operating surface that produces spaced entry andexit points of tangency with said surface for each direction ofmovement, and wherein movement of the tape over said operating surfacegenerates a fluid bearing between said tangency points, the improvementin means for providing a uniform bearing over a substantial portion ofsaid operating surface between said points of tangency for eachdirection of tape motion, comprising a slot, extending transversely ofthe direction of tape motion, immediately adjacent said exit point oftangency, within a distance from said exit point corresponding to ashort length of apparently rigid tape, and substantially longer than thetape width for supplying ambient fluid pressure between the tape and theoperating surface when the tape is moving in a direction toward saidexit point of tangency from the entry point of tangency
 2. The inventiondefined in claim 1, wherein the transverse slot has a cross-sectionalarea sufficient to produce ambient fluid pressure throughout its volume.3. The invention defined in claim 2, wherein there are two of said slotsextending transversely of the direction of tape motion and positionedbetween the spaced-apart entry and exit points of tangency.
 4. Theinvention defined in claim 3, wherein the magnetic tape is aconventional one-half-inch-wide record tape of average stiffness,wherein the radius portion of the operating surface has a radius of lessthan one inch, and wherein the angle of wrap is less than 10*.